Although the mammalian spinal cord may be the best studied of central neural systems, a large number of essential details of motoneuron and spinal interneuronal function still require clarification. Rational treatment of neurological disorders depends on knowledge of normal central neuronal function; it is felt that mastering and exploiting a mammalian spinal cord slice preparation will help elucidate these problems. One obvious advantage of this preparation is the accessibility of the cells to changes in external environments, and ionic contributions to transmitter release, the motoneuron spike, voltage-dependent repolarization, resting potential, voltage-insensitive hyperpolarizing afterpotential, resting membrane conductances, anomalous and delayed rectification, and electrotonic length of the dendrites will be studied. The divalent tonic requirements for "spontaneous" and evoked synaptic activity will be investigated, and when adequate concentrations of these cations for abolition of synaptic activity are determined, solution changes whose effects are only postsynaptic can be utilized. The effects of bath and iontophoretically applied glycine, GABA, glutamate, aspartate, acetycholine, nor-epinephrine, taurine and substance P will be determined as well as their ionic sensitivities. Evaluation of dendritic properties will be carried out and correlated with morphology determined after intracellular staining. Extracellular current fields of dendrites of single, morphologically studied neurons will be carried out and used to increase the probability of impaling dendritic elements at some distance from the soma. This will allow evaluation of current theories of dendritic function.